Bottom Line:
Label-free and real-time single-molecule detection may aid the development of high-throughput biosensing platforms.We found increased current oscillations synchronous to electric field excitations of characteristic molecular vibrational modes that contribute to inelastic electron tunnelling.This finding demonstrates a large contribution of charge interaction with nuclear dynamics on noise properties of single-molecule bridges and suggests a potential use of inelastic noise as a valuable molecular signature for single-molecule identification.

ABSTRACTLabel-free and real-time single-molecule detection may aid the development of high-throughput biosensing platforms. Molecular fluctuations are a source of noise that often hinders single-molecule identification by obscuring the fine details of molecular identity. In this study, we report molecular identification through direct observation of quantum-fluctuation-induced inelastic noise in single organic molecules. We investigated current fluctuations flowing through a single molecule that is chemically connected to two electrodes. We found increased current oscillations synchronous to electric field excitations of characteristic molecular vibrational modes that contribute to inelastic electron tunnelling. This finding demonstrates a large contribution of charge interaction with nuclear dynamics on noise properties of single-molecule bridges and suggests a potential use of inelastic noise as a valuable molecular signature for single-molecule identification.

Mentions:
To elucidate the underlying mechanism responsible for the electric-field-induced conductance fluctuations in single HDT molecules, we carried out consecutive 50 current measurements per Vb condition at a sampling rate of 30 Hz during a bias sweep in a range of −0.38 V≤Vb≤0.38 V (Fig. 1e) and examined their average current <I> and current noise σ (Fig. 1f). <I> is plotted as a function of Vb in Figure 2a. We obtained linear <I>–Vb characteristics analogous to the I–Vb curve shown in Figure 1c. Subtracting the elastic tunnelling current Ie from <I> yields the inelastic component Δ<I>=<I>–Ie11,12. We estimated Ie from a linear fit to the <I>–Vb curve in a low bias range of −0.005 V≤Vb≤0.005 V; nonlinearity of elastic tunnelling contributions is anticipated to be negligibly small because of the relatively high tunnelling barrier at the electrode–molecule links expected for the insulating molecular wire of HDTs (Supplementary Fig. S4). By extrapolating linear Ie–Vb to high biases (dotted line in Fig. 2a), we extracted Δ<I> and plotted with respect to Vb (Fig. 2b). The fact that /Δ<I>/ rises above 0 A with increasing Vb implies opening of active inelastic channels, rendering an increase in transmission of HDT molecules11,12,13.

Mentions:
To elucidate the underlying mechanism responsible for the electric-field-induced conductance fluctuations in single HDT molecules, we carried out consecutive 50 current measurements per Vb condition at a sampling rate of 30 Hz during a bias sweep in a range of −0.38 V≤Vb≤0.38 V (Fig. 1e) and examined their average current <I> and current noise σ (Fig. 1f). <I> is plotted as a function of Vb in Figure 2a. We obtained linear <I>–Vb characteristics analogous to the I–Vb curve shown in Figure 1c. Subtracting the elastic tunnelling current Ie from <I> yields the inelastic component Δ<I>=<I>–Ie11,12. We estimated Ie from a linear fit to the <I>–Vb curve in a low bias range of −0.005 V≤Vb≤0.005 V; nonlinearity of elastic tunnelling contributions is anticipated to be negligibly small because of the relatively high tunnelling barrier at the electrode–molecule links expected for the insulating molecular wire of HDTs (Supplementary Fig. S4). By extrapolating linear Ie–Vb to high biases (dotted line in Fig. 2a), we extracted Δ<I> and plotted with respect to Vb (Fig. 2b). The fact that /Δ<I>/ rises above 0 A with increasing Vb implies opening of active inelastic channels, rendering an increase in transmission of HDT molecules11,12,13.

Bottom Line:
Label-free and real-time single-molecule detection may aid the development of high-throughput biosensing platforms.We found increased current oscillations synchronous to electric field excitations of characteristic molecular vibrational modes that contribute to inelastic electron tunnelling.This finding demonstrates a large contribution of charge interaction with nuclear dynamics on noise properties of single-molecule bridges and suggests a potential use of inelastic noise as a valuable molecular signature for single-molecule identification.

ABSTRACTLabel-free and real-time single-molecule detection may aid the development of high-throughput biosensing platforms. Molecular fluctuations are a source of noise that often hinders single-molecule identification by obscuring the fine details of molecular identity. In this study, we report molecular identification through direct observation of quantum-fluctuation-induced inelastic noise in single organic molecules. We investigated current fluctuations flowing through a single molecule that is chemically connected to two electrodes. We found increased current oscillations synchronous to electric field excitations of characteristic molecular vibrational modes that contribute to inelastic electron tunnelling. This finding demonstrates a large contribution of charge interaction with nuclear dynamics on noise properties of single-molecule bridges and suggests a potential use of inelastic noise as a valuable molecular signature for single-molecule identification.